The photoelectrocatalytic (PEC) reduction of CO2 into high-value chemicals is beneficial in alleviating global warming and advancing a low-carbon economy. In this work, Pt-modified reduced graphene oxide (Pt-RGO) and Pt-modified TiO2 nanotubes (Pt-TNT) were combined as cathode and photoanode catalysts, respectively, to form a PEC reactor for converting CO2 into valuable chemicals. XRD, XPS, TEM, AFM, and SEM were employed to characterize the microstructures of the Pt-RGO and Pt-TNT catalysts. Reduction products, such as C2H5OH and CH3COOH, were obtained from CO2 under band gap illumination and biased voltage. A combined liquid product generation rate (CH3OH, C2H5OH, HCOOH, and CH3COOH) of approximately 600 nmol/(h·cm(2)) was observed. Carbon atom conversion rate reached 1,130 nmol/(h·cm(2)), which were much higher than those achieved using Pt-modified carbon nanotubes and platinum carbon as cathode catalysts.

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CO 2 synergistic reduction in a photoanodedriven photoelectrocatalytic (PEC) cell was conducted with a Pt-modified TiO 2 nanotube (Pt-TNT) photoanode and a Ptmodified reduced graphene oxide (Pt-RGO) electrocathode to reduce energy consumption and increase CO 2 PEC reduction efficiency. The carbon atom conversion rate of CO 2 reduction under PEC conditions was 2.3 times higher than that of the total rate under photocatalytic and electrocatalytic conditions. Synergistic CO 2 reduction in the PEC cell was mainly due to the use of the photoanode, which played a dual role during CO 2 reduction: (1) anode photovoltage compensated and conferred more negative cathode potential for CO 2 reduction and (2) anode water decomposition provided protons and electrons for cathode CO 2 reduction. System current density, product generation rate of CO 2 reduction, and carbon atom conversion rate increased first and then decreased with increasing deposition amount of Pt on TNT. The optimal photocatalytic activity of the Pt-TNT anode was obtained with a Pt loading amount of 5%, which resulted in the highest system current density of 4 mA/cm 2 and carbon atom conversion rate of 1250 nmol/(h cm 2 ) under the catalysis of the Pt-RGO cathode.

Cu foam combined with Pt-modified reduced graphene oxide (Pt-RGO) was investigated as an efficient cathode for CO 2 reduction in a photoelectrocatalytic (PEC) cell with a TiO 2 nanotube (TNT) photoanode. The synergistic catalytic mechanisms between photocatalysis and electrocatalysis in such a photoanode driven 2-electrode PEC cell were experimentally verified and theoretically analyzed. The dual functional Cu foam, as cathode electrode and Pt-RGO catalyst matrix, markedly increased the carbon atom conversion rate because of its well-defined porosity, large specific surface area, and in particular its affinity for CO 2 reduction to hydrocarbons. Combination of Cu foam matrix and Pt-RGO catalysts resulted in synergistic CO 2 reduction in the (Pt-RGO/Cu foam)||TNT PEC cell. Carbon atom conversion rate markedly increased to 4340 nmol/(h cm 2 ) by optimizing CO 2 reduction conditions in the PEC cell, including voltage applied through cell, Pt loading amount on RGO, and Pt-RGO loading amount on Cu foam. plants 1, 2 . However, CO 2 reduction into fuels is anticipated to be very challenging because of the necessary energy-consuming process consisting of multiple number proton-coupled electron-transfer steps 3, 4 . Recently, photoelectrocatalytic (PEC) systems for CO 2 reduction 5-8 have been widely studied as a promising approach to overcoming the high energy barrier of CO 2 conversion in an energy-efficient and environment friendly manner.The key point of CO 2 PEC reduction is to achieve a synergistic effect between photocatalysis and electrocatalysis.However, studies virtually concentrate on photo-enhanced electric-reduction or electric-enhanced photo-reduction previously 9 . The combination of photocatalysis and electrocatalysis doesn't achieve a real sense of synergistic function actually. Nowadays, research on the photo and electric synergistic catalytic reduction of CO 2 mainly focuses on semiconductor photocatalyst materials 10, 11 . Although some achievements have been made, CO 2 PEC reduction still suffers from low reactivity, low selectivity, and large energy consumption.The principle of PEC systems is based on the conversion of light energy into electricity within a cell involving two electrodes, of which at least one is made of a semiconductor. This electricity is then used for CO 2 conversion.In theory, there are three options for the arrangement of photo-electrodes in the assembly of PEC cells: (ⅰ) photocathode made of p-type semiconductor and anode made of metal 5, 6, 10, 11 ; (ⅱ) photoanode made of n-type semiconductor and cathode made of metal 7, 12, 13 ; (ⅲ) photoanode made of n-type semiconductor and photocathode made of p-type semiconductor 8 . The first use of photoelectrocatalysis for CO 2 reduction was reported over 30 years ago with a p-type photocathode in the first assembly form 14 . This photocathode driven form is simple, easy to manipulate and most widely studied. However, studies on this form are limited to the development and improvement of semiconductor catalysts responding to visible lig...

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